Water harvesting is collecting rainwater or run off water in catchment areas and maintaining the quality of this water. Often, this is related to collecting rainwater for direct consumption or to recharge groundwater with the water collected during the rains. Water harvesting can be termed as the process to make optimum use of water, be it the primary source i.e. rain or the secondary sources such as the groundwater, rivers, and lakes.

The amount of water that can be harvested is directly linked to the amount of rainfall and the collection efficiency of the catchments and various other factors such as spillage, water wastage, and evaporation.